1. Field of the Invention
The present invention relates to a display control apparatus and, more particularly, to a display control apparatus for controlling a display monitor used in a computer system such as a personal computer.
2. Description of the Related Art
In general, as display monitors for computer systems such as personal computers CRT display, or flat panel displays such as a liquid crystal display and a plasma display are used. At present, these displays are controlled using display controllers called VGA (Video Graphics Array) display controllers.
For this reason, a large number of application programs started on a computer system are formed to be suitable for the VGA specifications. In the VGA display controller, a mode of simultaneously displaying a maximum of 256 colors in 640.times.480 pixels and the like are prepared.
However, advanced operations using a high-saturation screen as in DTP (Desk Top Publishing) are requested for recent computer systems. For this reason, the resolution and the number of display colors provided by the VGA display controller have not been suitable for these advanced operations.
Therefore, in a recent computer system, a display controller of XGA (Extended Graphics Array) specifications or SVGA (Super Video Graphics Array) specifications having a display mode capable of realizing a display having a resolution higher than that of the VGA specifications begins to be used. In the display controller of the XGA specifications, since a high-resolution mode or the like of 1024.times.768 pixels is prepared, a large number of windows can be displayed on the same screen. For this reason, the display controller of the XGA specifications can be used to perform DTP operations, and can satisfactorily provide performance required for a graphical user interface which frequently uses a window display.
In the display controller, in order to cope with different resolutions of the XGA and VGA specifications, a switching operation between a high-resolution display of 1024.times.768 pixels and an intermediate-resolution display of 640.times.480 pixels is performed using a multi-sync CRT display. In this case, both high-resolution data and intermediate-resolution data are displayed on an entire display screen in a full-screen mode by a synchronous process in the CRT display.
However, when application programs of the XGA and VGA specifications are simultaneously executed, and the screen data of these application programs are alternately switched to be displayed, and screens having different resolutions are frequently switched to each other, flicker may disadvantageously occur on a display screen, depending on a CRT display, each time the switching operation is performed.
When intermediate-resolution data is displayed on the CRT display in a high-resolution mode, the problem of flicker occurring in relation to synchronism can be solved. However, in this case, the intermediate-resolution data is displayed at the corner of the screen, and visual recognition for the data is degraded. This problem is also posed when intermediate-resolution data of 640.times.480 pixels is displayed on a flat panel display having a high-resolution screen of 1024.times.768 pixels. In this case, the display position of the intermediate-resolution data is fixed to a specific position on the high-resolution screen, and this display position cannot be changed by the designation of a user.